Summary The Bighorn Helicopters Eurocopter AS350 D, C-FBHX, serial number 1428, and pilot were working for Alberta Environment near Blairmore, Alberta, providing support for weather station maintenance and snow pack analysis. An approach to a weather station site in mountainous terrain was made in strong, gusty winds. At about 50 to 100 feet above the mountainside landing site, an updraft and then a downdraft were encountered. The pilot aborted the landing and turned downhill but was unable to stop the sink rate as the helicopter settled into the trees and rolled onto its right side. The pilot and the front seat passenger received serious injuries, the rear passenger received minor injuries, and the helicopter was substantially damaged. The time of the accident was approximately 1115 mountain standard time. Ce rapport est galement disponible en franais. Other Factual Information The helicopter was contracted by Alberta Environment to transport two technicians to service two weather stations in the Crowsnest Pass area. Accompanying the technicians were a reporter and a cameraman from a Lethbridge television station. The pilot departed the company home base at Cranbrook, British Columbia, at 0830 mountain standard time1, and flew to Blairmore, Alberta, where he picked up four passengers. The flight departed Blairmore at about 0930 for the Allison Pass weather station. After the tasks at Allison Pass were completed, the helicopter then flew to the South Racehorse Creek weather station. Elevation at the station site is about 6300feet above sea level (asl). Following a reconnaissance flight to assess the wind and other conditions at the intended landing area on the east side of a mountain, the pilot decided to take two passengers into the site at a time. He dropped two passengers off at a cut block at the base of the mountain and flew the other two passengers back to the station. Because there was no flat place to land, the pilot toed the front of the helicopter skids onto the mountainside and kept the helicopter under power as the passengers disembarked, then departed down the mountain for the other two passengers. On the second approach to the station site, there were variable winds and the helicopter's airspeed indications were erratic. Just before landing, when at a height of 50to 75feet above the trees and slowing to hover speed, a gust lifted the helicopter. The pilot lowered the collective to maintain the descent, but the helicopter then suddenly began to descend at an excessive rate. The pilot aborted the approach and turned left down the slope away from the mountain. He reportedly did not raise the collective, but noticed that the main rotor rpm was indicating in the yellow arc (below normal operating range) on the tachometer. The low rotor warning horn sounded momentarily after the turn, but stopped when the pilot lowered the collective slightly. He then raised the collective to increase power for a climb and the engine accelerated, but the helicopter continued to descend. It settled into the trees and came to rest in deep snow, laying on its right side facing north. The television cameraman in the right rear seat recorded the accident sequence from after the turn until an impact dislodged the camera and it departed the helicopter. Total time of the recording was about five seconds. The 1200 weather report for the Cranbrook Airport , 45nautical miles (nm) west of the accident site, was as follows: wind 170true at13, gusting to 24knots; visibility 25statute miles (sm); a few clouds at 5000feet and broken clouds at 6000feet. The upper winds at 6000feet were forecast to be from 220 at 21knots with a temperature of 1C. The Pincher Creek Airport autoweather, 25nm east, was reporting winds from 260 at 30 gusting to 44knots, sky clear, and temperature of 5C. The Lethbridge Airport, 50nm east, was reporting winds from 240 at 32gusting to 42knots, visibility of 30sm, a few clouds at 12000feet, and broken cloud at 25000feet. The forecast upper winds at Lethbridge at 6000feet were 42knots, with a temperature of 1C. Mountain Wave activity was seen in satellite photos, and moderate lee wave turbulence was forecast for the region. Passengers described the turbulence as average given the wind conditions. Depending on the slope and surrounding terrain, downdrafts from 21-knot winds could reach speeds of 2100feet per minute (fpm) down, from 32-knot winds, speeds of 3250 fpm down, and from 42-knot winds, speeds of 4250fpm down. The engine, a Lycoming LTS-101-600A3, serial numberLE43442CE, did not initially appear to respond when increased power was commanded. No unusual indications or sounds were noticed from the engine. The video tape recorded the sounds of the engine accelerating after the turn. The engine continued to run for a short time after the helicopter came to rest. After the occurrence, the engine was shipped to the manufacturer and a full operational test was completed in the manufacturer's test cell, attended by a Federal Aviation Administration (FAA) inspector and the operator's representatives. The engine met all the specifications as to power output, acceleration, and throttle response. A check of the engine records did not reveal any history of problems with the fuel control unit, power turbine governor, or engine fuel pump. Main rotor head and blade examination revealed damage consistent with considerable power being produced when the rotor blades contacted trees. The main rotor operating speed is 385rpm, the yellow arc on the tachometer is between 320and 370rpm, and the low rotor warning horn is set to activate at a speed between 270and 335rpm. The helicopter had no known deficiencies before the flight and was being operated within its load and centre of gravity limits. The calculated gross weight of the helicopter was 3640pounds. For this weight, at 55knots airspeed, at an ambient air temperature 1C, and at an altitude of 6300feet, the helicopter's maximum rate of climb was computed to be about 1500fpm. The pilot was certified and qualified for the flight in accordance with existing regulations. He had about 2460hours total flight time, with about 2220hours in helicopters, of which 170hours were on type. He had completed a 15-hour mountain flying course, and had about 780hours of mountain flying experience, of which about 100hours were on type. His last single-engine pilot proficiency check (PPC) was on a BellB206 on 27April2001.